1. Field of the Invention
The present invention relates to a semiconductor wafer regenerating system and method and, more specifically, to a system and method for removing patterns formed on a semiconductor wafer to enable the reuse of the semiconductor wafer.
2. Description of Related Arts
Semiconductor integrated circuit (IC) chips being present in everyday electrical and electronic devices are created through a multiple-step sequence of photographic and chemical processing steps, during which electronic circuits are gradually created on a wafer made of pure semiconductor material. Reviewing the semiconductor device fabrication in more detail, extremely pure semiconductor material (e.g., silicon) is grown into mono-crystalline cylindrical ingots, and the ingots are then sliced into wafers about 0.75 mm thick and polished to obtain a very flat surface. Once the wafers are prepared, transistors are formed on the silicon water using various processing steps, e.g., chemical vapor deposition, etching, photolithography, and diffusion and/or ion implantation. After the various semiconductor devices have been created, they are interconnected to form the desired electrical circuits by metal interconnecting wires.
Considering the highly serialized nature of wafer processing, between the various processing steps, wafer tests are performed to verify that the wafer is still good and haven't been damaged by previous processing steps. If the number of die (i.e., a potential chip portion) on a wafer that measure as fails exceed a predetermined threshold, the wafer is discarded rather than invest in further processing. On the other hand, after the metal interconnections are completed, the semiconductor devices are subjected to a variety of electrical tests to determine if they function properly. The device test is carried out using tiny probes, which marks bad chips with a drop of dye. In case that the yield which represents the proportion of devices on the wafer found to perform properly is high enough, the wafer is broken into individual dice, each of which is bonded on a lead frame and packaged. If, however, the yield is below a predetermined threshold, the wafer is discarded.
The discarded wafers which failed to pass the wafer test or device test retains circuit patterns and cannot be used for another purpose, and thus are typically crushed into pieces and scrapped under the ground. Such disposal of discarded wafers results in waste of expensive resources, wafer, and may bring about environment contamination. Accordingly, a method for recycling the discarded wafers is strongly needed.
Some attempts have been made for recycling the discarded wafers. For example, U.S. Pat. No. 6,706,636 issued 16 Mar. 2004 to Renesas Technology Corp. and entitled METHOD OF REGENERATING SEMICONDUCTOR WAFER discloses a method of regenerating a semiconductor wafer using mixed acids. According to this method, a wafer is polished and then immersed in mixed acids. Afterwards, a surface treatment is performed on the wafer to planarize the surface of the wafer, and then a high temperature annealing process is performed to ultimately obtain a regenerate wafer. However, the disclosed method may be inefficient in that not so few process steps are involved in the regenerating process, which makes this method time-consuming. Further, simply polishing and immersing the wafer in mixed acids cannot guarantee the complete removal of ion-implanted region showing physical characteristics different from that of pure silicon and trenches deeply formed into the surface. Besides, the use of several kinds of acids increases the cost for regenerating the wafer.
U.S. Patent Application Publication No. US2005/0092349 published 5 May 2005 and entitled METHOD OF RECLAIMING SILICON WAFERS discloses a method of regenerating a semiconductor wafer through consecutive steps of etching, polishing, and heat-treatment. Among the various steps, this attempt is focused on the heat-treatment of the wafer for 20 minutes-5 hours. As a result, this method may be much more time-consuming and inefficient.
As mentioned above, the conventional methods show low productivity in regenerating semiconductor wafers and are costly due to the use of a large quantity of chemicals and abrasives. Thus, the prior art wafer regenerating techniques provide little benefit from the economic point of view.